A vector-symbiont method is used to alter vector competence in the reduviid bug Rhodnius prolixus. The symbiont Rhodococcus rhodnii has been genetically altered to express a pore-forming peptide, cecropin-A in the hindgut of R. prolixus in the proximity to the Chagas' disease-causing trypanosome, Trypanosoma cruzi. Preliminary data show that cecropin-A expression causes elimination or considerable reduction of T. cruzi numbers in the hindgut rectal ampullae and the fecal droplets of the bug. The proposed work will determine if the intra-gut expression of cecropin-A eliminates or reduces Chagas' disease transmission from bug to mouse (a) under laboratory conditions (b) under closed simulated field conditions. A proprietary method (fully described in the application) has been devised to spread the cecropin-A-expressing transgene throughout R. prolixus populations and will be tested in the laboratory and in closed simulated field trials. The effect of environmental and gut-associated bacterial fauna on disease transmission and transgene spreading will be determined.